Photovoltaic is the field of technology, which directly converts sunlight to electricity. The solar cell is the elementary building block of the photovoltaic (PV) technology. Solar cells are made of semiconductor materials, such as silicon. One of the properties of the semiconductors that makes them most useful is that their conductivity may easily be modified by introducing impurities into their crystal lattice. On one side of the cell the impurities, which are phosphorus atoms with five valence electrons, on the other side, atoms of boron with three valence electrons create a greater affinity than silicon to attract electrons.
The layers of the photovoltaic cells made of semiconductor materials, which should be light responsive. The materials include Group I-III-VI, Group IV and Group III-V, as well as II-VI semiconductor materials, such as CdTe, CdSe, CdS, CdO, ZnS, and so on.
Chanyawadee, S. et al, fabricate a hybrid nanocrystal quantum-dot patterned p-i-n structure that utilizes nonradioactive energy transfer from highly absorbing colloidal nanocrystal quantum dots to a patterned semiconductor slab to demonstrate a six fold increase of the photocurrent conversion efficiency compared to the bare p-i-n semiconductor device. The heterostructure was grown by molecular beam epitaxy on a (100) GaAs substrate in a p-i-n configuration that consists of 20 periods of 7.5 nm thick GaAs quantum wells with 12 nm thick AlGaAs barriers, (Physical Review Letters, 102, 077402, 2009.
In another article by Chanyawadee, S. et al, (Applied Physics Letters, 94, 233502, 2009), demonstrate photocurrent enhancement of a hybrid PV device consisting of highly absorbing colloidal Nanocrystals (NC) and a patterned bulk p-i-n heterostructure at both low 25 K and room temperature. The patterning is designed to bring the colloidal NCs into close proximity with the intrinsic region of the p-i-n heterostructure so that the excitation energy of the deposited NCs is efficiently transferred to the patterned bulk p-i-n heterostructure by means of nonradiative energy transfer. This hybrid NC/bulk p-i-n device offers about two orders of magnitude higher photocurrent than the hybrid NC/Quantum Well p-i-n PV device from their previous work above and releases the potential of high efficiency PV cells and optoelectronic devices.
Kiravittaya, S. et al, proposes Quantum Dots (QD) using InGaAs on InAs of size 40-50 nm in diameter and 4-7 nm in height to be used for PV applications because of its wider spectral response, better temperature stability and possibility of carrier storage feature, (PV Conference 2000, 28th IEEE Conf., P 818-821, 2000).
Patent application (WO 2008/137995) discloses an improved photovoltaic devices and methods. A photovoltaic device includes a semiconductor layer and a light-responsive layer which form a junction, such as a p-n junction. The light-responsive layer can include a plurality of carbon nanostructures, such as carbon nanotubes, located therein. In many cases, the carbon nanostructures can provide a conductive pathway within the light-responsive layer. In other photovoltaic devices include semiconductor nanostructures, which can take a variety of forms, in addition to the carbon nanostructures. Methods of fabricating photovoltaic devices are also disclosed.
Another Patent application US 2008/0216894 A1 suggests Nanostructures and quantum dots are used in photovoltaic cells or solar cells outside of the active layer to improve efficiency and other solar cell properties. In particular, organic photovoltaic cells can benefit. The quantum dot layer can be found between the light source and the active layer or on the side of the active layer opposite the light source. Quantum dots can also be used in electrode layers.
A prior art suggests several QD layers to be deposited in the active layer of the solar cell having several bandgaps and Fermi levels. Particularly, the size and composition of a QD can determine its bandgap and Fermi level, (US 2009/0255580 A1).
Patent application (US 2008/0130120 A1) suggests nanostructured layers absorbing IR and/or UV in a photovoltaic device increases efficiency of solar cells. The nanostructure materials are integrated with one or more of: crystalline silicon (single crystal or ponlycrystalline) solar cells and thin film (amorphous silicon, microcrystalline silicon, CdTe, CIGS and III-V materials) solar cells whose absorption is primarily in the visible region. The nanoparticle materials are comprised of quantum dots, rods or multipods of various sizes.